By Dr. David A. Summers, Curators’ Professor at Missouri University of Science & Technology
Wandering the aisles at the IMTS and Fabtech trade shows that bring the latest tools to the attention of the manufacturing industry, there is always a group of folk standing watching the cutting demonstrations. The waterjet cutting booths in particular have always seemed to attract more of a crowd over the course of the day, and the relative quiet where you can still talk as you stand by the waterjet table is, perhaps, one of the benefits that waterjet technology has brought as it grows increasingly popular. It similarly does not hurt when the demonstration involves cutting those show trinkets which can, after a quick rinse, be given as a souvenir and reminder of the tool capabilities.
The introduction of high-pressure waterjet jets into the industry was not quite that high tech, since it had been discovered quite early in the technical history that waterjets at a pressure of around 5,000psi/350 bar were quite effective in removing the burrs left when parts are machined conventionally. (Robert Burns has since written that the test of jet effectiveness is that it can be used when a 0.5 mm lead in a mechanical pencil will move the burr, rather than breaking the lead). (http://www.processcleaning.com/articles/water-jet-deburring-for-complex-metal-parts). The water jet stream had the advantage, over mechanical probes, that they could also bounce around corners in the parts, thereby reaching regions more difficult to clear. The de-burring step can be eliminated in many processes today by integrating a high-speed waterjetting in with the cutting tool in conventional machining. However tool design and integration has proceeded much further in the larger-scale mining and excavation industry than in metal cutting, where it remains still as more of a demonstration in a University laboratory than a tool that has become established in the market-place, even though it has been shown to make it possible to machine even difficult materials).
Yet the de-burring example shows one of the advantages that high-pressure water jet cutting has demonstrated in growing applications over the years. The highly focused force of the jet, when properly placed on the target cuts without significant damage along either edge of the cut surfaces left afterwards. The early examples of this (and one of the first commercial successes) was in the cutting of cardboard, where the jet will cut across the sheet without crimping the edges, which keeps the strength of the box edge that would otherwise be lost.
In a similar way, when abrasive is added to the waterjet stream so that it can cut through metals, glass and other ceramic materials (such as those used in computer chips and similar applications), the cut surfaces that are left are unchanged by the cutting process. The heat-affected-zone that is induced with thermal and mechanical tool cutting is removed, and the local stresses induced in thicker material as it is cut or milled are much reduced, so that there is less distortion around the cutting path, and in any narrow ribs of material left either in the part, or the material separating pieces in the initial sheet. This, again, is more critical in thicker parts, where an abrasive jet can be used to outline the final shape of a milled pocket, for example, before the mechanical tool removes the central material, so that, in this way, a very narrow rib around the pocket can be left undistorted by the stresses imposed by the mechanical tool.
And the lack of a de-burring step remains since, in contrast with more mechanical cutting processes, two parts can be located and fixed together in their final alignment, before cutting fastener holes between them. The fasteners (whether rivets, or bolts) can then be inserted and made tight without the need to take the pieces apart to remove the residual burrs that would otherwise develop on both pieces of metal.
There are, in short, a variety of different ways in which the opportunities for business that a high-pressure waterjet cutting table brings can be developed. Some of these opportunities come from learning what is already being done in other aspects of waterjet technology, and some are unique to this application. Some of these ideas are well known, and others less so. But to try and cover them in a single article is difficult, which is why I will be writing this KMT Waterjet Technology Blog posted on www.kmt-waterjet.com. It is meant to give, at about five hundred to a thousand words a week, a more detailed explanation and background to why some things work, and others don’t, as well as thoughts on where the waterjet industry can grow. I look forward to the KMT Waterjet Weekly Waterjet Blog Series.